As is well known, various processes and catalysts exist for the homopolymerization or copolymerization of α-olefins. For many applications it is of primary importance for a polyolefin to have a high molecular weight while having a relatively narrow molecular weight distribution. It is further desirable to have a catalyst, which within reasonable ranges of ethylene to α-olefin monomer ratios, will catalyze the incorporation of higher (up to 50% by weight) contents of α-olefin comonomers in the production of ethylene-α-olefins copolymers.
Japanese patent application JP6080683 describes unbridged monocyclopentadienyl group 4-6 metal compounds, which are said to provide benefits for propylene polymerization, and exemplifies the production of atactic polypropylene with cyclopentadienyl bistrimethylsilylamide titanium dichloride, activated with methylalumoxane at 40° C.
U.S. Pat. No. 5,625,016 discloses catalyst systems based on an unbridged monocyclopentadienyl group 4 metal compound having a bulky group 15 ligand, which is suitable for the preparation of ethylene-α-olefin copolymers of high molecular weight at high temperatures in solution, with ready incorporation of α-olefins. Examples of ethylene-propylene copolymerization at 115° C. with cyclopentadienyl bis-trimethylsilylamide titanium dimethyl/dimethylanilinium tetra(perfluorophenyl)borate show polymers with up to 30% by weight propylene incorporation, but in a low yield.
U.S. Pat. No. 6,063,879 describes a class of (unbridged) monocyclopentadienyl group 4 metal phosphinimides. Such complexes are suitable for ethylene homo and ethylene-α-olefin copolymerization by solution or gasphase polymerization at high temperature.
Further, U.S. Pat. No. 6,114,481, which represents the most relevant prior art document, discloses a class of group 4 methyl compounds having a ketimide ligand as catalyst component for the preparation of polymers of high molecular weight and low density. More specifically the catalyst comprises a metallocene compound of formula CyLMZ2, wherein M is a group 4 metal, L is a ketimide ligand, (a ketimide group is a group having formula —N═C<), Cy is a cyclic ligand, having a delocalized π-bond with the group 4 metal, such as a cyclopentadienyl group, and two activation reactive ligands Z.
The ketimide ligand L of this known compound contains two bulky carbyl substituents: wherein Sub1 and Sub2 are preferably tert.butyl groups.
Ketimide titanium complexes were already prepared by Latham et al., (J. Chem. Soc., Dalton Trans. 1986, 377), but not tested in an olefin polymerization process.
Zhang et al., (J. Am. Chem. Soc., 2000, 122, 5499-5509) studied the thermal stability of dialkyls of the Cp(L)Ti fragment (wherein Cp is a cyclopentadienyl group and L is a ketimide ligand of formula N═CRR1), activated by B(C6F5)3.